For a vapor return line, I don't think you need to go back to the tank.
As long as you plumb back to a cool fuel source, it should work fine in an auto gas carbeurated scenario. This is not the same as a fuel return for a FI system.
Possible options would be to return it to the fuel selector, if you have plugged up one of the inlets, or primer. Or, just put a T in the fuel line somewhere.
All you are doing is giving the vaporized gas a place to go, other than into the carb, and then be able to condense in a cooler environment. Remember, the return line should have a restrictor in it, because you only want the vapor to flow into it, where you T off near the carb inlet. The return line can be smaller than the fuel line, in diameter, for this reason.
I have used a system like this and it worked for me after I had vapor lock problems under a hot cowl, using MoGas. (FYI - The vapor usually occurred after a flight, some heat soaking from sitting, and then when you put in the power for take off it would start sputtering due to vapor in the lines. Winter gas on a warm day was especially vulnerable. However, mixing avgas (~20%) along with MoGas will also usually fix the problem.)
